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Publications

  1. M. Niehle, J.-B. Rodriguez, L. Cerutti, E. Tournie, A. Trampert
    Acta Materialia, Volume 143, 15 January 2018, Pages 121-129
    On the origin of threading dislocations during epitaxial growth of III-Sb on Si(001): A comprehensive transmission electron tomography and microscopy study

    Abstract

    Electron tomography and complementary (scanning) transmission electron microscopy (STEM) are applied to investigate the origin of threading dislocations in the large lattice misfit, heteroepitaxial system of III-Sb on vicinal Si(001). Buried AlSb islands of the initial wetting layer are revealed at the interface toward the substrate in the three-dimensionally reconstructed data. Locations of island coalescence are retrieved from the tomogram. Complementary (S)TEM measurements reveal the location of threading dislocations and the presence of antiphase boundaries at the same specimen area. The number density of threading dislocations emanating from the interface and their distribution are unexpected. It is shown that the presence of threading dislocations is not simply correlated to sites of AlSb-islands coalescence or to the film closure during the transition from a 3D to a 2D growth. Moreover, an interaction with antiphase boundaries is suggested by the presented observations. Consequently, the contemporary notion of threading dislocation formation is refined and, eventually, it is suggested that measures to avoid antiphase domains and such to reduce threading dislocations have to be balanced for future strategies to epitaxially grow sphalerite structure III-V semiconductors on Si or Ge.
  2. M. Niehle, A. Trampert, J.B. Rodriguez, L. Cerutti, E. TourniƩ
    Scripta Materialia, Volume 132, 15 April 2017, Pages 5-8
    Electron tomography on III-Sb heterostructures on vicinal Si(001) substrates: Anti-phase boundaries as a sink for threading dislocations

    Abstract

    The three-dimensional arrangement of threading dislocations in a III-Sb based mid-infrared laser structure is studied by electron tomography (in a scanning transmission electron microscope). The stack of planar antimonide films which are grown by molecular beam epitaxy on vicinal Si(001) substrates, exhibits an inhomogeneous distribution of threading dislocations. A strong interaction of these line defects with planar defects is revealed. A significant number of dislocations appears to be trapped in anti-phase boundaries which are predominantly parallel to (110) lattice planes. Based on this finding, an explanation for the inhomogeneous distribution of dislocations is established.
  3. M. Niehle, A. Trampert
    Micron, Volume 73, June 2015, Pages 54-62
    Electron tomography on nanopores embedded in epitaxial GaSb thin films

    Abstract

    This work reports on the morphology of nanopores and their spatial position in group III-Sb based multilayer heterostructures grown by molecular beam epitaxy on Si(0 0 1) substrates. By using electron tomography based on dark-field scanning transmission electron microscopy, quantitative information in real space is obtained about individual nanopores unintentionally embedded in GaSb layers. For this purpose adequate needle-shaped samples have to be specifically prepared from the compact material system by focused ion beam. The three-dimensional reconstruction of the probed volume allows the determination of the spatial arrangement of the pores and the analysis of the detailed shape, i.e. the crystallographic facets. Based on these results, the nanopore's geometric shape is discussed with respect to the minimization of surface tension. The formation process can be explained by an agglomeration of vacancies which are generated during the heterostructure growth.
  4. M. Niehle, A. Trampert, S. Albert, A. Bengoechea-Encabo, E. Calleja
    APL Materials 3, Volume 3, February 2015, 036102
    Electron tomography of (In,Ga)N insertions in GaN nanocolumns grown on semi-polar (112-2) GaN templates

    Abstract

    We present results of scanning transmission electron tomography on GaN/(In,Ga)N/GaN nanocolumns (NCs) that grew uniformly inclined towards the patterned, semi-polar GaN(112-2) substrate surface by molecular beam epitaxy. For the practical realization of the tomographic experiment, the nanocolumn axis has been aligned parallel to the rotation axis of the electron microscope goniometer. The tomographic reconstruction allows for the determination of the three-dimensional indium distribution inside the nanocolumns. This distribution is strongly interrelated with the nanocolumn morphology and faceting. The (In,Ga)N layer thickness and the indium concentration differ between crystallographically equivalent and non-equivalent facets. The largest thickness and the highest indium concentration are found at the nanocolumn apex parallel to the basal planes.